Class 9 Biology MCQs: Plant Physiology

MCQs (sample)

Showing 25 questions from this chapter. For a full timed test, use “Start online test”.

1. 1. What is a nutrient?

   • A substance that provides necessary elements for growth and metabolism
   • A substance only required in large quantities
   • A type of plant organ
   • A type of organic compound
   Answer & explanation

   Correct: A substance that provides necessary elements for growth and metabolism

   A nutrient is defined as any substance that provides necessary elements to the organism for growth and metabolism.

2. 2. What is gaseous exchange in plants primarily responsible for?

   • Providing oxygen for cellular respiration
   • Producing glucose
   • Absorbing nutrients from the soil
   • Regulating water levels in cells
   Answer & explanation

   Correct: Providing oxygen for cellular respiration

   Gaseous exchange ensures that plants receive oxygen needed for cellular respiration.

3. 3. What are the three levels of transport in plants?

   • From outside to inside, within the plant, and from inside to outside
   • Only from leaves to roots
   • From flowers to leaves
   • Only from roots to fruits
   Answer & explanation

   Correct: From outside to inside, within the plant, and from inside to outside

   The three levels of transport in plants involve movement from outside to inside, within the plant body, and from inside to outside.

4. 4. What is homeostasis in plants?

   • Adjustment to environmental changes in temperature and water availability
   • Growth of plants in different climates
   • Absorption of water and salts from soil
   • Storage of organic compounds
   Answer & explanation

   Correct: Adjustment to environmental changes in temperature and water availability

   Homeostasis in plants refers to how they adjust to varying degrees of environmental temperatures and the availability of water and salts in the soil.

5. 5. What type of nutrients do plants mainly absorb?

   • Organic nutrients
   • Inorganic nutrients
   • Mineral nutrients
   • Energy nutrients
   Answer & explanation

   Correct: Inorganic nutrients

   Plants mainly absorb inorganic nutrients from the environment, including water, carbon dioxide, and certain minerals.

6. 6. What are the two main openings through which gaseous exchange occurs in plants?

   • Stomata and roots
   • Lenticels and stomata
   • Lenticels and petals
   • Leaves and flowers
   Answer & explanation

   Correct: Lenticels and stomata

   Gaseous exchange mainly occurs through stomata and lenticels in plants.

7. 7. What is the primary site for absorption of water and minerals in plants?

   • Root hairs
   • Leaf stomata
   • Stem nodes
   • Fruit skin
   Answer & explanation

   Correct: Root hairs

   Root hairs are the primary sites for the absorption of water and minerals.

8. 8. Why is homeostasis important for plants?

   • It helps them grow taller than other plants
   • It allows them to survive, grow, and reproduce
   • It makes them resistant to all diseases
   • It ensures they use sunlight effectively
   Answer & explanation

   Correct: It allows them to survive, grow, and reproduce

   Homeostasis in plants is essential for survival, growth, and reproduction, enabling them to adapt to environmental changes.

9. 9. How many elements are considered essential for plant growth?

   • Nine
   • Sixteen
   • Seven
   • Twelve
   Answer & explanation

   Correct: Sixteen

   Sixteen elements have been found essential for plant growth.

10. 10. During the day, what gas do plants inhale for photosynthesis?

    • Oxygen (O2)
    • Carbon dioxide (CO2)
    • Nitrogen (N2)
    • Methane (CH4)
    Answer & explanation

    Correct: Carbon dioxide (CO2)

    During the day, plants inhale carbon dioxide (CO2) for photosynthesis.

11. 11. What are Casparian strips?

    • Deposits of wax in endodermal walls
    • Types of root hairs
    • Openings in the leaves
    • Parts of the xylem
    Answer & explanation

    Correct: Deposits of wax in endodermal walls

    Casparian strips are deposits of wax (suberin) found in the radial walls of endodermal cells.

12. 12. What waste product do plants excrete during the night?

    • Oxygen
    • Carbon dioxide
    • Water
    • Sugars
    Answer & explanation

    Correct: Carbon dioxide

    Carbon dioxide is excreted by plants at night during the gaseous exchange process as a waste of respiration.

13. 13. What are macronutrients?

    • Elements required in very small amounts
    • Elements required in large quantities
    • Only organic compounds
    • Non-essential nutrients
    Answer & explanation

    Correct: Elements required in large quantities

    Macronutrients are the nutrients required in large quantities (greater than 0.05% dry weight).

14. 14. What is released by plants during the daytime as a result of photosynthesis?

    • Carbon dioxide (CO2)
    • Nitrogen (N2)
    • Oxygen (O2)
    • Hydrogen (H2)
    Answer & explanation

    Correct: Oxygen (O2)

    Plants release excess oxygen (O2) during daytime as a result of photosynthesis.

15. 15. Which process actively transports minerals against their concentration gradient?

    • Facilitated diffusion
    • Osmosis
    • Active transport
    • Diffusion
    Answer & explanation

    Correct: Active transport

    Active transport requires energy (ATP) and moves minerals against their concentration gradient.

16. 16. How do plants excrete water?

    • Through photosynthesis
    • Via transpiration
    • By consuming it
    • Through respiration
    Answer & explanation

    Correct: Via transpiration

    Water is excreted by plants through the process of transpiration, which occurs when water evaporates from the plant body.

17. 17. Which of the following is NOT a macronutrient?

    • Calcium
    • Iron
    • Potassium
    • Nitrogen
    Answer & explanation

    Correct: Iron

    Iron is a micronutrient and is required in small amounts (less than 0.05% dry weight).

18. 18. At nighttime, how do plants behave in terms of gas exchange?

    • They inhale carbon dioxide and exhale oxygen
    • They inhale oxygen and exhale carbon dioxide
    • They do not exchange gases
    • They continue photosynthesis
    Answer & explanation

    Correct: They inhale oxygen and exhale carbon dioxide

    At nighttime, plants inhale oxygen and exhale carbon dioxide because there's no photosynthesis happening.

19. 19. What does transpiration primarily help with in plants?

    • Photosynthesis
    • Absorbing water and dissolved minerals
    • Producing seeds
    • Root growth
    Answer & explanation

    Correct: Absorbing water and dissolved minerals

    Transpiration helps absorb water and dissolved minerals, moving them upwards to leaves.

20. 20. What is meant by osmoregulation in plants?

    • Absorption of nutrients
    • Maintaining water and solute balance
    • Photosynthesis process
    • Growth in response to light
    Answer & explanation

    Correct: Maintaining water and solute balance

    Osmotic adjustment, or osmoregulation, refers to how plants maintain the right balance of water and solutes in their bodies.

21. 21. What is the major source of nitrates in the soil?

    • Decomposition of dead organic matter
    • Rainwater absorption
    • Plant growth
    • Soil erosion
    Answer & explanation

    Correct: Decomposition of dead organic matter

    The major source of nitrates in the soil is the decomposition of dead organic matter.

22. 22. What happens during dawn and dusk regarding gas exchange in plants?

    • Photosynthesis occurs but no respiration
    • Both processes equal each other, resulting in no net exchange
    • Respiration stops completely
    • Plants absorb more nitrogen than oxygen
    Answer & explanation

    Correct: Both processes equal each other, resulting in no net exchange

    During dawn and dusk, the rates of photosynthesis and respiration become equal, resulting in no net exchange of gases.

23. 23. How does temperature affect the rate of transpiration?

    • It has no effect
    • It increases transpiration up to a point but then may cause stomatal closure
    • It always decreases transpiration
    • It only affects transpiration at night
    Answer & explanation

    Correct: It increases transpiration up to a point but then may cause stomatal closure

    Higher temperatures generally increase transpiration, but extreme heat can cause stomata to close.

24. 24. Which group of plants lives in water-rich environments?

    • Xerophytes
    • Mesophytes
    • Hydrophytes
    • Drought-resistant plants
    Answer & explanation

    Correct: Hydrophytes

    Hydrophytes are plants that thrive in water-rich environments.

25. 25. What is the most obvious symptom of nitrogen deficiency in plants?

    • Wilting of leaves
    • Chlorosis (yellowing of leaves)
    • Stunted growth
    • Browning of stems
    Answer & explanation

    Correct: Chlorosis (yellowing of leaves)

    Chlorosis, or yellowing of plant leaves, is the most obvious symptom of nitrogen deficiency in plants.